This invention relates generally to self-expanding endovascular stents for use in preventing restenosis of passageways and ducts in the body, to repair aneurysms percutaneously, and also for dilating recurring stenosis immediately after attempts with ballooning.
This invention represents an improvement in the self-expanding stents described and shown in U.S. Pat. No. 4,580,568 to Gianturco. Conventional stents of this type include a wire formed in a closed zigzag configuration that includes an endless series of straight sections joined by bends. A conventional zigzag stent is resiliently compressible into a small diameter such that the straight sections are arranged side by side and closely adjacent one another for insertion into a passageway. The stent is resiliently self-expandable into a larger second diameter wherein the straight sections press against the walls of the passageway to maintain it open. Although conventional zigzag stents have proven quite useful in many situations, their performance characteristics tend to decrease as the length of the stent increases.
Self-expanding stents are normally evaluated with respect to four performance characteristics: the radially outward expansile force that the stent exerts on the vascular wall; the small diameter to which the stent is capable of being compressed for the insertion procedure; the ability of the stent to adapt to curved passageways in the patient's body; and the stability of the stent in not migrating from its originally implanted position within the patient.
Conventional zigzag stents must normally be made relatively short because the straight wire sections prevent the stent from readily adapting to curves in the passageway of a patient. Furthermore, the expansile force of conventional zigzag stents generally decreases with the length of the stent. One solution to these drawbacks has been to modify the conventional zigzag stent by connecting a plurality of shorter stents end on end to create one longer zigzag stent assembly. Although these modified zigzag stents represent an improvement over conventional zigzag stents for certain applications, there exists a need for an elongated self-expanding stent that includes the advantages of both conventional and modified zigzag stents but which has improved performance characteristics over both.
The present invention also represents an improvement over the self-expanding spiral stents described in U.S. Pat. No. 5,019,090 to Pinchuk. Pinchuk teaches the production of an elongated zigzag pattern by spirally wrapping a wire about an oblong mandrel, removing the mandrel, and then flattening the spiral to produce an elongated zigzag band. The elongated zigzag band is then spirally wrapped around a cylindrical mandrel to produce the stent. One drawback to the Pinchuk design, however, is that all of the elongate member's that make up the zigzag pattern have equal lengths. The result being that a bisector of the angle defined by each pair of elongated members is not parallel to the central axis of the finished stent. This causes the stent to undesirably distort in shape when radially compressed for the implantation procedure. What is needed is a spiral zigzag stent in which a bisector of each pair of elongated members is parallel to the central axis of the finished stent. Such a stent cannot be produced by the method for making stents taught by Pinchuk.